Auxiliary cam phaser hydraulic circuit and method of operation

ABSTRACT

Provided is an auxiliary cam phaser hydraulic circuit for an internal combustion engine having an engine driven hydraulic pump and at least one cam phaser in fluid communication with a cam phaser control valve. The auxiliary cam phaser hydraulic circuit includes a reservoir containing fluid and an auxiliary hydraulic pump in fluid communication with the reservoir and operable to pressurize the fluid and communicate the fluid under pressure to a cam phaser feed passage. The cam phaser feed passage is in fluid communication with the cam phaser control valve, which operates to selectively and variably communicate the fluid to the cam phaser. A method of starting and operating an internal combustion engine is also provided. An internal combustion engine incorporating the auxiliary cam phaser hydraulic circuit is also disclosed.

TECHNICAL FIELD

The present invention relates to internal combustion engines employing hydraulically actuated cam phasers and more specifically to hydraulic circuits operable to actuate the hydraulically actuated cam phasers.

BACKGROUND OF THE INVENTION

Internal combustion engines may employ valvetrain components to vary intake and/or exhaust valve timing to control or optimize engine performance and efficiency. Among the various types of variable valve timing devices are camshaft phasing devices, or cam phasers, often in the form of drive pulleys and the like, incorporating phase changing means for varying the phase between a rotatable input drive member such as a gear, pulley, or sprocket, and a coaxial rotatable output driven member such as a camshaft. An exemplary cam phaser mechanism is described in U.S. Pat. No. 5,588,404 issued Dec. 31, 1996, which is assigned to the assignee of the present invention and is hereby incorporated by reference in its entirety.

Cam phaser mechanisms are typically hydraulically actuated against the bias force of a spring to vary the phasing of a camshaft attached thereto. A control valve is typically provided in fluid communication with the cam phaser and operates to control the cam phaser by selectively and variably providing pressurized fluid to actuate the cam phaser. The spring urges the cam phaser into a default or “parked” position in the absence of fluid pressure. The parked position is typically selected to enable the internal combustion engine to start under extreme low ambient air temperatures, such as −40 degrees Celsius. The park position enables high effective compression ratios to enable combustion with cold ambient air temperatures. This park position is typically not the optimized engine starting position for higher ambient air temperatures since the effective compression ratio at startup can be reduced with the increased ambient air temperature.

Pressurized fluid, typically in the form of engine oil, is communicated to the cam phaser via the oiling or lubrication circuit of the internal combustion engine. A positive displacement hydraulic pump communicates pressurized fluid to a main lubrication passage of the lubrication circuit. The hydraulic pump is typically driven by the internal combustion engine and, as such, does not provide pressurized fluid to the cam phasers prior to starting the internal combustion engine. Therefore, the ability to phase the camshafts to a position better suited to starting the internal combustion engine prior to ignition may be lacking.

Additionally, once the internal combustion engine is started, a minimum threshold engine speed is typically required to provide the cam phasers with the requisite fluid flow and pressure for actuation. This threshold engine speed may be as high as 800 to 1,000 RPM, which for many internal combustion engine applications is above idle speed. Therefore, the camshaft phasing may not be optimized during idle operation of the internal combustion engine.

SUMMARY OF THE INVENTION

Accordingly, an auxiliary cam phaser hydraulic circuit for an internal combustion engine having an engine driven hydraulic pump and at least one cam phaser in fluid communication with a cam phaser control valve is provided. The auxiliary cam phaser hydraulic circuit includes a source containing fluid and an auxiliary hydraulic pump in fluid communication with the source. The auxiliary hydraulic pump operates to pressurize the fluid and communicate the fluid under pressure to a cam phaser feed passage. The cam phaser feed passage is in fluid communication with the cam phaser control valve. The cam phaser control valve operates to selectively and variably communicate the fluid to the cam phaser to effect actuation.

The auxiliary hydraulic pump may be driven by an electric motor, which is controlled by an electronic control unit. Additionally, the electronic control unit may be preprogrammed to command the cam phaser control valve to enable the at least one cam phaser to enable one of late intake valve closing and early intake valve closing to enable a reduction in effective compression ratio during starting of the internal combustion engine. A main lubrication passage operable to receive the fluid from the engine driven hydraulic pump may also be provided. The main lubrication passage is in selective fluid communication with the cam phaser feed passage. A check valve may be configured to selectively communicate the fluid from the main lubrication passage to the cam phaser feed passage and to substantially disallow communication of the fluid from the cam phaser feed passage to the main lubrication passage. Alternately, the auxiliary pump may be configured to provide the fluid under pressure to the main lubrication passage via the cam phaser feed passage.

A method of starting and operating an internal combustion engine having at least one hydraulically actuatable cam phaser and an engine driven hydraulic pump is also provided. The method includes providing pressurized fluid to the at least one hydraulically actuatable cam phaser when the internal combustion engine is shutoff. Additionally, the method includes controlling the at least one hydraulically actuatable cam phaser to command the internal combustion engine to operate in one of a late intake valve opening and an early intake valve opening mode of operation and subsequently starting the internal combustion engine.

The method may further include continuing to provide pressurized fluid to the at least one hydraulically actuatable cam phaser during engine operation between idle engine speed and a threshold engine speed. The threshold engine speed may be the engine speed below which the engine driven hydraulic pump cannot provide the required fluid flow and pressure to actuate the at least one hydraulically actuatable cam phaser.

The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial schematic illustration of an internal combustion engine illustrating an auxiliary cam phaser hydraulic circuit consistent with the present invention; and

FIG. 2 is a method, in flow chart form, of starting and operating the internal combustion engine shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown a schematic illustration of a portion of an internal combustion engine, generally indicated at 10. The internal combustion engine 10 includes a cylinder bank 12 having a plurality of cylinders 14. A plurality of hydraulic lash adjusters 16 cooperate with an intake camshaft 18, a portion of which is shown in FIG. 1, through a valve actuation mechanism, not shown, to provide a measured amount of air or air and fuel to the cylinders 14 for combustion therein. Additionally, a plurality of hydraulic lash adjusters 20 cooperate with an exhaust camshaft 22, a portion of which is shown in FIG. 1, through a valve actuation mechanism, not shown, to exhaust products of combustion from the cylinders 14. Mounted to the intake camshaft 18 is an intake cam phaser 24. Similarly, mounted to the exhaust camshaft 22 is an exhaust cam phaser 26. Those skilled in the art of engine design will recognize that the intake and exhaust cam phasers 24 and 26 operate to vary the intake valve timing and the exhaust valve timing, respectively.

The internal combustion engine 10 is a four-stroke engine having an intake stroke, compression stroke, expansion or power stroke, and exhaust stroke. During the intake stroke, air and fuel are introduced to the cylinders 14 as a piston (not shown), which is reciprocally disposed therein, moves from a top dead center position to a bottom dead center position. During the compression stroke, the air and fuel are compressed by the piston moving from the bottom dead center position to the top dead center position. During the power stroke, the air and fuel are combusted and the rapidly expanding products of combustion force the piston to move from the top dead center position to the bottom dead center position. During the exhaust stroke, the products of combustion are pushed from the cylinder 14 as the piston moves from the bottom dead center position to the top dead center position. Those skilled in the art will recognize that the timing of the intake valve opening event will influence the amount of air introduced to the cylinders 14.

The internal combustion engine 10 further includes a sump or reservoir 28, such as an oil pan, operable to contain a volume of fluid, such as engine oil 30. An engine driven hydraulic pump 32 operates to draw oil 30 from the reservoir 28 through a pickup tube 34. The engine driven hydraulic pump 32 is a positive displacement pump and communicates oil 30 under pressure to a filter 36. The filter 36 removes particulate matter from the oil 30 prior to entering a main oil passage 38. The main oil passage 38 operates to provide oil 30 to lubricate moving components within the internal combustion engine such as camshaft and main bearings, not shown. An orifice 40 is provided in a portion of the main oil passage 38 to limit the flow of oil 30 to a hydraulic lash adjuster feed circuit 42. The hydraulic lash adjuster feed circuit 42 includes a lash adjuster feed passage 44, which communicates oil 30 from the orifice 40 to each of the plurality of lash adjusters 20 and to a solenoid operated valve 46. As is well known to those skilled in the art, the plurality of hydraulic lash adjusters 16 and 20 utilize the pressurized oil within the hydraulic lash adjuster feed passage 44 to maintain proper clearances within the valve actuation components, not shown, of the internal combustion engine 10.

The plurality of hydraulic lash adjusters 16 are so called “switching” hydraulic lash adjusters. That is, the hydraulic lash adjusters 16 provide at least two distinctly different valve lifts depending on the fluid pressure of the oil 30 communicated to them. The solenoid actuated valve 46 selectively communicates both low and high pressure values of oil 30 to the plurality of hydraulic lash adjusters 16. With the solenoid actuated valve 46 in a first position, illustrated by valve portion 47 aligned with passage 44 as shown schematically in FIG. 1, the oil 30 within the hydraulic lash adjuster feed passage 44 must pass through an orifice 48 prior to entering a second hydraulic lash adjuster feed passage 50. The orifice 48 creates a reduced pressure valve for oil 30 within the second hydraulic lash adjuster feed passage 50 to enable the plurality of hydraulic lash adjusters 16 to provide a first valve lift value. Additionally, a pressure relief valve 52 will exhaust oil 30 to the reservoir 28 should an excess pressure value of oil 30 manifest within the second hydraulic lash adjuster feed passage 50. Alternately, with the solenoid actuated valve 46 in a second position, as shown schematically in FIG. 1 to illustrate valve portion 54 aligned with passage 44 (in phantom), the oil 30 within the hydraulic lash adjuster feed passage 44 is unrestrictedly communicated to the second hydraulic lash adjuster feed passage 50 to enable a second valve lift value.

A cam phaser feed passage 56 operates to communicate pressurized oil from the main oil passage 38 to a first and second cam phaser control valve 58 and 60, respectively. The first and second cam phaser control valves 58 and 60 operate to selectively and variably communicate oil 30 from within the cam phaser feed passage 56 to the respective intake cam phaser 24 and exhaust cam phaser 26 to effect actuation. The intake and exhaust cam phasers 24 and 26, in the absence of pressurized fluid in feed passage 56, will remain in a default or “parked” position.

In the absence of sufficient pressurized oil provided by engine driven hydraulic pump 32, i.e. when the engine is not running or pressure is too low, the present invention provides an auxiliary cam phaser hydraulic circuit 62 to enable actuation of the intake and exhaust cam phasers 24 and 26. The auxiliary cam phaser hydraulic circuit 62 includes an auxiliary hydraulic pump 64, which operates to draw oil 30 from the reservoir 28 and communicate the oil 30, under pressure, to the cam phaser feed passage 56 for subsequent communication to the first and second cam phaser control valves 58 and 60. A filter 65 operates to separate and remove particulate matter from the oil 30 prior to communicating the oil 30 to the cam phaser feed passage 56. The auxiliary cam phaser hydraulic circuit 62 enables the intake and exhaust cam phasers 24 and 26 to be operated or actuated in the absence of pressurized oil from the engine driven hydraulic pump 32. In the preferred embodiment, the auxiliary hydraulic pump 64 is operated by an electric motor 66. A check valve 68 may be included within the cam phaser feed passage 56 to substantially block or disallow the flow of oil 30 to the main oil passage 38 when the auxiliary hydraulic pump 64 is operating. However, the check valve 68 may be omitted to allow the auxiliary hydraulic pump 64 to provide pressurized oil to the main oil passage 38, thereby pressurizing the hydraulic lash adjuster feed circuit 42 and other lubrication circuits within the internal combustion engine 10 prior to starting the internal combustion engine 10. By supplying an amount of oil 30 to the internal combustion engine 10 via the auxiliary hydraulic pump 64, wear to the internal components of the internal combustion engine 10 during starting may be reduced.

An electronic control unit or ECU 70 is preferably operable to control the first and second cam phaser control valves 58 and 60, the electric motor 66, and the solenoid actuated valve 46 in response to inputs 72 from engine, transmission, and/or vehicle sensors, not shown. The ECU 70 preferably includes a programmable digital computer whose operation is known to those skilled in the art. Additionally, the ECU 70 may include lookup tables and an algorithm memory to enable precise control of the first and second cam phaser control valves 58 and 60 in response to the inputs 72.

The parked position of the intake and exhaust cam phasers 24 and 26 are typically chosen such that the internal combustion engine 10 will start at very low ambient air temperature conditions, such as −40 degrees Celsius. To enable this, the intake cam phaser 24 parks the intake camshaft 18 at a position that will allow the maximum amount of air to be introduced into the cylinders 14 during engine cranking. This maximizes the effective compression ratio of the engine. The effective compression ration of an internal combustion engine is generally understood to be the compression ratio of an engine when cranking or running and can vary from the geometric compression ratio, which is calculated using dimensional values of the internal combustion engine. The effective compression ratio is sensitive to variations in intake valve timing. By introducing the maximum amount of air into the cylinders of the internal combustion engine 10, the in-cylinder pressures will increase during the compression stroke, thereby increasing the temperature within the cylinders 14 to enable efficient combustion of fuel at such low ambient air temperatures.

As the ambient air temperature increases, the effective compression ratio required to enable efficient starting of the internal combustion engine 10 can be reduced. Therefore, by actuating the intake cam phaser 24 prior to starting the internal combustion engine to enable a late intake valve closing (LIVC) or an early intake valve closing (EIVC) engine operating mode, the effort required to start the internal combustion engine 10 may be reduced. The LIVC operating mode phases the intake camshaft 18 to allow the intake valves of the internal combustion engine 10 to remain open later into the compression stroke of the engine than is typical. Thus, a portion of the air drawn into the cylinders 14 is allowed to be pushed out of the cylinders 14 to reduce the amount of air compressed within the cylinders 14 during the compression stroke. Alternately, the EIVC operating mode phases the intake camshaft 18 to allow the intake valves of the internal combustion engine 10 to close early in the intake stroke of the engine than is typical. Thus, the amount of air drawn into the cylinders 14 is reduced thereby reducing the amount of air compressed within the cylinders 14 during the compression stroke. The auxiliary cam phaser hydraulic circuit 62 enables movement of intake and exhaust cam phasers 24 and 26 when the internal combustion engine 10 is shut off. Preferably, the ECU 70 is preprogrammed to command the first cam phaser control valve 58 to phase the intake cam phaser 24 to one of an LIVC and an EIVC operating mode when the internal combustion engine 10 is shutoff to reduce the starting effort through the reduction in compression. A more detailed description of utilizing cam phasers to enable an LIVC and EIVC operation mode is provided in U.S. Pat. No. 6,843,214 issued Jan. 18, 2005, which is assigned to the assignee of the present invention and is hereby incorporated by reference in its entirety.

The reduction in starting effort of the internal combustion engine 10 is especially beneficial for so-called “mild hybrid” vehicles, not shown. Such mild hybrid vehicles operate using an “idle stop” mode of operation. In operation, when the mild hybrid vehicle is at rest and the internal combustion engine 10 is idling, such as at a stop light, the internal combustion engine 10 is automatically shut off to conserve fuel. Subsequently, when the operator requires the vehicle to move, the internal combustion engine 10 is automatically commanded to restart. It is preferred that the restarting of the internal combustion engine 10 is as imperceptible to the operator as possible.

The auxiliary hydraulic pump 64 may be operated during idle stop modes to allow the intake cam phaser 24 to command the intake camshaft to a LIVC or EIVC position to reduce the starting effort of the internal combustion engine 10. By reducing the starting effort of the internal combustion engine 10, the noise, vibration, and harshness (NVH) associated with engine restart may be reduced. Additionally, the size of the starter or combined alternator starter to restart such vehicles may be reduced as a result of the reduced starting effort.

The intake and exhaust cam phasers 24 and 26 typically require a threshold oil flow and pressure in order to effect actuation. This oil flow and pressure is typically unobtainable at low engine speeds such as idle or during warm up of the internal combustion engine 10 when the viscosity of oil 30 is high. By employing the auxiliary cam phaser hydraulic circuit 62 in concert with the engine driven hydraulic pump 32 during low engine speeds and during warm up of the internal combustion engine 10, the ability to actuate the exhaust and intake cam phasers 24 and 26 is maintained. By operating both the auxiliary hydraulic pump 64 and the engine driven hydraulic pump 32, the intake and exhaust camshafts 18 and 22 can be phased to enable optimal operating conditions for the internal combustion engine 10.

Referring now to FIG. 2, and with continued reference to FIG. 1, there is shown an exemplary method 74 of operating the internal combustion engine 10. Preferably, the ECU 70 would be preprogrammed to operate the internal combustion engine 10 in accordance with the method 74. The method 74 begins at step 76. At step 76, the auxiliary hydraulic pump 64 is commanded by the ECU to operate, thereby providing oil 30, under pressure, to the cam phaser feed passage 56 to enable operation of the intake and exhaust cam phasers 24 and 26. The method then proceeds to step 78 where the ECU commands the intake cam phaser 24 to enable the internal combustion engine 10 to operate in one of an LIVC and EIVC operating mode, thereby placing the internal combustion engine 10 in a more favorable condition for starting.

The method 74 then proceeds to step 80 where a determination is made as to whether the internal combustion engine 10 has been commanded to start. If a start command has not been made by the ECU 70, the method 74 will loop to step 76. Alternatively, if the ECU 70 has commanded the internal combustion engine 10 to start, the method 74 will proceed to step 82 where the internal combustion engine 10 is started. At step 84, the auxiliary hydraulic pump 64 will continue to provide oil 30 to the cam phaser feed passage 56 to enable actuation of the intake and exhaust cam phasers 24 and 26. The method 74 then continues to step 86 where a determination is made as to whether the speed of the internal combustion engine 10 is at or below a threshold speed. This threshold engine speed as discussed hereinabove is the engine speed below which the fluid flow and pressure, provided by the engine driven hydraulic pump 32, to the intake and exhaust cam phasers 24 and 26 is too low to effect actuation of the intake and exhaust cam phasers 24 and 26. If the threshold engine speed has not been attained, the method 74 will loop to step 84 and the auxiliary hydraulic pump will remain operating to provide oil 30 to the cam phaser feed passage 56 to enable actuation of the intake and exhaust cam phasers 24 and 26. Alternatively, if the threshold engine speed has been attained, the method 74 will proceed to step 88 and the ECU 70 will discontinue operation of the auxiliary hydraulic pump 64. At this point, the flow and pressure of oil 30 provided by the engine driven hydraulic pump 32 is sufficient to actuate the intake and exhaust cam phasers 24 and 26. Those skilled in the art will recognize other parameters that may be used in lieu of engine speed to determine the proper switching point between the operation of the auxiliary hydraulic pump 64 and the engine driven hydraulic pump 32 such as, for example, oil temperature.

While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims. 

1. An auxiliary cam phaser hydraulic circuit for an internal combustion engine having an engine driven hydraulic pump and at least one cam phaser in fluid communication with a cam phaser control valve, the auxiliary cam phaser hydraulic circuit comprising: a source containing fluid; an auxiliary hydraulic pump in fluid communication with said source and operable to pressurize said fluid and communicate said fluid under pressure to a cam phaser feed passage; and wherein said cam phaser feed passage is in fluid communication with the cam phaser control valve, the cam phaser control valve being operable to selectively and variably communicate said fluid to said cam phaser.
 2. The auxiliary cam phaser hydraulic circuit of claim 1, wherein said auxiliary hydraulic pump is driven by an electric motor.
 3. The auxiliary cam phaser hydraulic circuit of claim 2, further comprising an electronic control unit operable to control said electric motor.
 4. The auxiliary cam phaser hydraulic circuit of claim 1, further comprising an electronic control unit operable to control the cam phaser control valve.
 5. The auxiliary cam phaser hydraulic circuit of claim 4, wherein said electronic control unit is preprogrammed to command the cam phaser control valve to enable the at least one cam phaser to enable one of late intake valve closing and early intake valve closing to enable a reduction in effective compression ratio during starting of the internal combustion engine.
 6. The auxiliary cam phaser hydraulic circuit of claim 1, further comprising: a main lubrication passage operable to receive said fluid from the engine driven hydraulic pump; wherein said main lubrication passage is in selective fluid communication with said cam phaser feed passage; and a check valve configured to selectively communicate said fluid from said main lubrication passage to said cam phaser feed passage and to substantially disallow communication of said fluid from said cam phaser feed passage to said main lubrication passage.
 7. The auxiliary cam phaser hydraulic circuit of claim 1, further comprising: a main lubrication passage operable to receive said fluid from the engine driven hydraulic pump; wherein said main lubrication passage is in fluid communication with said cam phaser feed passage; and wherein said auxiliary pump is configured to provide said fluid under pressure to said main lubrication passage via said cam phaser feed passage.
 8. A method of starting and operating an internal combustion engine having at least one hydraulically actuatable cam phaser and an engine driven hydraulic pump, the method comprising: providing pressurized fluid to the at least one hydraulically actuatable cam phaser when the internal combustion engine is shutoff; controlling said at least one hydraulically actuatable cam phaser to command the internal combustion engine to operate in one of a late intake valve opening and an early intake valve opening mode of operation; and starting the internal combustion engine.
 9. The method of claim 8, further comprising: continuing to provide pressurized fluid to the at least one hydraulically actuatable cam phaser during engine operation between idle engine speed and a threshold engine speed.
 10. The method of claim 8, wherein an auxiliary hydraulic pump provides pressurized fluid to the at least one hydraulically actuatable cam phaser.
 11. The method of claim 9, wherein said threshold engine speed is the engine speed below which the engine driven hydraulic pump cannot provide the required fluid flow and pressure to actuate the at least one hydraulically actuatable cam phaser.
 12. The method of claim 9, further comprising: communicating pressurized fluid from the engine driven hydraulic pump to the at least one hydraulically actuatable cam phaser during engine operation above said threshold speed.
 13. An internal combustion engine comprising: an engine driven hydraulic pump; at least one cam phaser in fluid communication with a cam phaser control valve; a source containing fluid; an auxiliary hydraulic pump in fluid communication with said source and operable to pressurize said fluid and communicate said fluid under pressure to a cam phaser feed passage; and wherein said cam phaser feed passage is in fluid communication with the cam phaser control valve, the cam phaser control valve being operable to selectively and variably communicate said fluid to said cam phaser.
 14. The internal combustion engine of claim 13, wherein said auxiliary hydraulic pump is driven by an electric motor.
 15. The internal combustion engine of claim 14, further comprising an electronic control unit operable to control said electric motor.
 16. The internal combustion engine of claim 13, further comprising an electronic control unit operable to control the cam phaser control valve.
 17. The internal combustion engine of claim 16, wherein said electronic control unit is preprogrammed to command the cam phaser control valve to enable the at least one cam phaser to enable one of late intake valve closing and early intake valve closing to enable a reduction in effective compression ratio during starting of the internal combustion engine.
 18. The internal combustion engine of claim 13, further comprising: a main lubrication passage operable to receive said fluid from the engine driven hydraulic pump; wherein said main lubrication passage is in selective fluid communication with said cam phaser feed passage; and a check valve configured to selectively communicate said fluid from said main lubrication passage to said cam phaser feed passage and to substantially disallow communication of said fluid from said cam phaser feed passage to said main lubrication passage.
 19. The internal combustion engine of claim 13, further comprising: a main lubrication passage operable to receive said fluid from the engine driven hydraulic pump; wherein said main lubrication passage is in fluid communication with said cam phaser feed passage; and wherein said auxiliary pump is configured to provide said fluid under pressure to said main lubrication passage via said cam phaser feed passage. 